Preburning plant for burning solid fuel materials having a high ash contents

ABSTRACT

The preburning plant for burning solid fuel materials having a high ash contents, particularly barks or cut wood chips, is comprised of a hearth (10) downwardly delimited by a grid (15), supplied with fuel material by a hopper (6). The hearth (10) communicates with the boiler (2) by a combustion channel (11). Inside the cladding (9) and above the combustion channel (11), a vertical axis ring (19) is arranged above the grid (15) for fuel material degassing purposes. The ring is rotatingly driven, preferably periodically, so that an endless screw (26) conveys the fuel material to the hearth (10).

The invention refers to a pre-furnace heating plant for the combustionof solid combustible material of high ash content, in particular of barkand wood chips, which comprises a furnace chamber confined at its bottomby a grate and receiving the combustible material from above via astorage compartment, said furnace chamber being surrounded by a mantleof refractory material, a combustion channel connecting the furnacechamber with a succeeding boiler and extending through the mantle andhaving an opening for supplying secondary air, in the mantle there beingprovided a further opening for supplying primary air below the grate,this further opening being preferably closeable by means of a controlflap being controlled by the boiler.

It is known that various combustible materials of high ash content, inparticular wood bark, wood chips from sawmills and from agriculture, andalso wet garbage, can not be burned in normal boilers for centralheatings, because due to the permanent cooling effect of the heatcarrier fluid (water) flowing through the mantle of the boiler, thefurnace chamber can not be brought to the temperature required for thecombustion of such a combustible material. Thus, a prefurnace burningequipment of the initially described type has become known for burningsuch a combustible material, which equipment is connected with itscombustion channel to the furnace chamber of the central-heating boilerwhich acts as a heat exchanger. It is a drawback of the known equipmentthat frequently the combustible material forms an arch within thestorage compartment and that the equipment can only be maintainedoperative for a short time interval of approximately one hour, whereuponthe whole equipment must be cleaned on account of the highcontent in ashand in noxious matter of the combustible material, in particular woodbark. This operation is laboursome and troublesome and, in addition, noheat is supplied to the central-heating boiler during the cleaningperiod.

It is an object of the present invention to avoid the mentioneddrawbacks and to improve a pre-furnace heating equipment of theinitially described type such that arching within the storagecompartment and thus also disturbances of the combustion process areavoided, and that also the efficiency of the equipment and theutilization of the combustible constituents of the combustible materialare substantially improved. The invention solves this task by the factthat a gasifier ring is provided within the mantle and at a distanceabove the grate, which gasifier ring has an upright axis and has its topsurface inclined in direction towards its central opening, and a wormmember extending in direction towards this opening, said gasifier ringbeing rotatable around its axis by a drive means, so that the wormmember conveys the combustible material through the opening of thegasifier ring. By this relative movement between gasifier ring and worm,the combustible material resting on the gasifier ring over a relativelylarge area is reliably taken along for rotation and is conveyed by theworm into the furnace chamber so that the combustible material locatedwithin the storage compartment and above the gasifier ring is loosenedup and any arching of this material is destroyed, so that thecombustible material is reliably fed into the furnace chamber. Thus itis ensured that always a sufficient amount of combustible material ispresent within the furnace chamber and that the combustion proceeds tothe desired extent. It is thus not only avoided that the first withinthe furnace chamber is extinguished, but the furnace chamber or itswall, respectively, are always maintained at the temperature mostfavourable for the combustion process, which is just of importance forthe combustion of problematic combustible material, in particular woodbark. Preferably, the worm member extends through the opening of thegasifier ring, whereby also an arching or bridging of the combustionmaterial within the gasifier ring can be reliably avoided. The wormmember can also be driven for rotation, but according to a preferredembodiment of the invention it is more favourable in view of a reducedexpenditure, if the worm member is stationary and is held at its upperend by a rod located within a hollow shaft connected to the gasifierring to the drive means for the gasifier ring. This arrangement isparticularly efficient and of simple construction. The rod holding theworm member and the hollow shaft support themselves one against theother. Intermittent rotation of the gasifier ring is energy-saving andis, as a rule, sufficient for reliably providing the furnance chamberwith combustible material and for avoiding troublesome arching. Bygeared motor it is easy to achieve the desired rotational speed of thegasifier ring.

An advantageous further development of the invention consists in thatthe hollow shaft is provided within the storage compartment withlaterally protruding projections, for example with resilient prongs.These projections loosen the combustible material within the storagecompartment and contribute to avoid arching of the combustible material.

A preferred embodiment of the invention consists in that the gasifierring can be lifted and lowered for changing its distance from the grate.In this manner, the volumetric capacity of the furnace chamber can bevaried, which provides a further possibility for the control of theequipment in addition to the control of the supply of primary air andsecondary air particularly from the draught regulator of the boiler. Thementioned height adjustment of the gasifier ring can be effected withoutany problems and with an only low energy expenditure by lifting orlowering, respectively, the hollow shaft.

Rotation of the gasifier ring can, however, also be used for a furtherpurpose: If, according to the invention, a grate scraper is providedbetween the grate and the gasifier ring which grate scraper rotatesrelatively to the grate, this results in stripping residues off thegrate, so that the grate need be cleaned only less frequently.Preferably, the grate scraper comprises at least one bar sliding overthe grate. In this case, the arrangement may be such that the gratescraper has vertical rods being longitudinally guided within openings ofthe gasifier ring. This simple construction ensures that the gratescraper is reliably taken along when rotating the gasifier ring andallows height adjustment of the gasifier ring at any time. However, thegrate can also be coupled with the gasifier ring and the grate rotate,while the grate scraper remains stationary. According to a simpleconstruction this can be achieved by providing the grate with verticalrods which are guided in openings or peripheral grooves of the gasifierring for longitudinal motion in order to allow the mentioned heightadjustment of the gasifier ring. For making the worm member fullyeffective also in the uppermost position of the gasifier ring, i.e. ifthe furnace chamber has its maximum volumetric capacity, the worm membermay, according to a further feature of the invention, extend in thelowermost position of the gasifier ring into the hollow shaft for thelength of the stroke of the gasifier ring. In this manner, effectivepitches of the worm member are at disposal even it the hollow shaft, andtherewith the gasifier ring, is lifted. The worm member may consist of ametal strip twisted around its longitudinal axis, which must onlyconsist of a material which is sufficiently temperature-resistent.

Further features and advantages of the invention can be seen from thedescription of embodiments of the invention which are schematicallyshown in the drawings.

FIG. 1 shows a first embodiment of the invention in a vertical section.

FIG. 2 is a section along line II--II of FIG. 1.

The FIGS. 3 and 4 show, in sections similar to FIG. 1, two modifiedembodiments.

The pre-furnace burning equipment 1 as shown in the FIGS. 1 and 2 islined up with a central-heating boiler 2 and is controlled by thedraught regulator 3 thereof in a manner to be later described in detail.The equipment 1 has a storage compartment 4 for receiving thecombustible material to be burned, in particular wood bark, saw dust,wood chips, but also domestic garbage (also wet, but without ceramic ormetallic components). This combustible material can optionally be mixedwith coal dust. The storage compartment 4 is confined by a housing 5expanding in upward direction like a funnel and being closed on its topby a cover wall 6. At the front side an opening 8 for charging thestorage shaft 4 is provided which opening 8 can be closed by means of acharging door 7. The housing 5 extends downwardly in the shape of acircular annular mantle 9 of refractory material, for example refractoryconcrete, which mantle encloses a furnace chamber 10 in which thecombustible material is burnt. A combustion channel 11 passing throughthe mantle 9 extends from the furnace chamber 10 to the boiler 2, saidcombustion channel being equally surrounded by a refractory mantle 12through which extends an opening 13 for the supply of secondary air. Theopening 13 can be closed by a lid 14.

The furnace chamber 10 is confined on its bottom by a grate 15 which hasthrough-passages for the ash, said passages being arranged around theaxis of the furnace chamber 10 along arcs of a circle, which ash fallsinto an ash chamber 16 which is accessible through an opening 18 withinthe mantle 9, said opening being closeable by means of a cleaning door17.

Within the circular mantle 9 and above the grate 15, spaced apart fromthis a gasifier ring 19 is provided which is arranged concentricallyrelative to the axis of the furnace chamber 10 and can be rotated aroundthis axis. For this purpose, the gasifier ring 19 is fixed to a hollowshaft 21 by means of struts 20, which hollow shaft extends upwardlywithin the storage compartment 4 and is supported for rotation and forbeing shiftable in longitudinal direction in the cover wall 6. Thishollow shaft 21 is driven for rotation by a geared motor 22 beingintermittently energized and deenergized by a time switch 23, so thatthe hollow shaft 21, together with the gasifier ring 19, isintermittently rotated. Within the interior of the hollow shaft 21 thereis located a rod 24 which is supported in a manner described later on indetail at its upper end by a head piece 25 of the geared motor 22. Thissupporting is later on described in detail in connection with FIG. 4. Atits lower end the rod 24 carries a worm member 26, the lower end ofwhich may be fixed to the grate 15, particularly then, if the wormmember 26 stands still. The hollow shaft 21 is height-adjustible bymeans of an adjusting gearing not shown and adjustable in the selectedposition so that the height position of the gasifier ring 19 within themantle 9 and therewith the height of the furnace chamber 10 locatedbelow the gasifier ring 19 can be adjusted.

A grate scraper 27 contacts the upper side of the grate 15 and has threebars 28 sliding over the grate 15 and extending radially in outwarddirection from a ring 29 surrounding the lower end of the worm member26. The outer ends of these bars 28 carry upwardly protruding carrierbolts 30, which extend through openings 31 of the gasifier ring 19 andare guided within these openings so that they can be shifted inlongitudinal direction. In this manner, the grate scraper 27 is takenalong for rotation as soon as the gasifier ring 19 is rotated andscrapes the grate 15 free of contaminations by means of the bars 28.

Primary air is supplied to the furnace chamber 10 through the grate 15from below, this air flowing through a passage 32 within the mantle 9and through the opening 18 into the ash chamber 16 and, respectively, tothe grate 15. The upper end of the passage 32 can be closed by a lid 33.Both lids 14, 33 are controlled by the draught regulator 3 of the boiler2 such that, in dependence on the boiler temperature, the lid 14controlling the supply of secondary air is closed and the lid 33controlling the supply of primary air is opened, or vice versa. Thecorresponding control lines 34 provided for this purpose areschematically indicated by dashed lines.

The combustible material charged into the storage compartment 4 via thecharging opening 8 accumulates within the storage shaft 4 above thegasifier ring 19. An account of the heat generated within the furancechamber 10 and within the combustion channel 11, the mantle 9 and thegasifier ring 19, equally consisting of refractory material, are heatedup to a comparatively high temperature, which results not only inpre-drying the combustible material located within the storagecompartment 4, but also in degasifying of at least those portions ofcombustible material which rest on the gasifier ring 19. A furtherpre-heating of the combustible material is achieved by the hot metallicworm member 26 which conducts the heat from the furnace chamber 10 tothe storage compartment 4. The thus generated gases are sucked by thedraught generated by the chimney via the central-heating boiler 2 andvia the combustion channel 11 into the combustion channel 11 and areburnt there. The required combustion air is supplied via the primary airchannel 32 and, respectively, or via the secondary air channel formed bythe opening 13. The degree of combustion within the furnace chamber 10can be controlled by the mentioned air supply from the draught regulator3 of the boiler 2, on the one hand, and by height adjustment of thegasifier ring 19, on the other hand. Arching of the combustible materialwithin the storage shaft 4 is reliably prevented on account of the factthat, on the one hand, the combustible material is at leastintermittently moved by the projections 35, having the shape ofresilient prongs horizontally protruding from the hollow shaft 1, andthat, on the other hand, the gasifier ring 19 forms a supporting surfacefor the combustion material which is intermittently rotated around itsvertical axis, so that the combustible material slides into the furnacechamber 10 along the top surface 37 of the gasifier ring 19 in directionto its central opening 36, which top surface is inclined toward thiscentral opening. In order to accumulate the combustible material in thefurnace chamber 10 as well as possible in the shape of a heap, thegasifier ring 19 is provided with a collar 38 extending downwardly fromits opening 36, which collar holds the combustible material togetherwhich slides into the furnace chamber 10. This collar 38 can be formedby a short tube.

The worm member 26 can in a simple manner be designed as a twisted metalstrip, which draws the combustible material, taken along for rotation bythe rotation of the gasifier ring 19, into the opening 36 of thegasifier ring 19. For better accomodating the upper end of the wormmember 26, the hollow shaft 21 can have a greater diameter in itslowermost portion accommodating this worm end.

The embodiment according to FIG. 3 differs from that according to theFIGS. 1 and 2 essentially only in the design of the gasifier ring 19, ofthe grate 15 and of the grate scraper 27. According to FIG. 3, thegasifier ring 19 consists of a hollow truncated cone, in particular of atemperature-resistent metallic or ceramic material. The volumetriccapacity of the furnace chamber 10 located below the gasifier ring 19 isthus increased within the marginal areas of the gasifier ring 19. In asimilar manner, the grate 15 is upwardly inclined in its marginal area,so that there results a central, trough-shaped depression for theburning material. Accordingly, also the radial bars of the grate scraper27 are upwardly inclined within the marginal area, so that the grate 15is cleaned over its total top surface.

The equipment can be provided with an additional worm conveying thecombustible material from a great storage container located outside ofthe housing 5 into said housing 5. As a precaution means againstburn-back, a sprinkler equipment known per se can be provided.

A further advantageous modified construction consists in that the grate15 is suspended on the worm 26 but is nevertheless arranged within themantle 9 for being movable in height direction. This provide thepossibility to lower the grate 15 by means of the worm member 26, forexample if a greater residual mass which can not be forced through thegrate openings, rests on the grate. In lowered position of the grate,the residual mass can be removed through the cleaning door 17. Loweringof the grate further provides the possibility to effect an additionalsupply of primary air above the grate 15.

The efficiency of an equipment according to the invention issubstantially higher, when compared with known equipments. No externalenergy is consumed with the exception of the energy required for theagitating movement and for moving the grate scraper, so that the energyrequirement is very low, because it is sufficient to move the gasifierring 19 and the grate scraper 27, respectively, for some seconds only intime intervals of approximately half an hour.

There are no difficulties to design the equipment for varying heatrequirement, approximately 10,000 and 100,000 heat units, the chimneydraught being sufficient and no additional measures being necessary forobtaining the draught.

It is also of advantage that the burn-up can be changed for at least 75percent between the minimum value and the maximum value, so that theequipment can even be operated in summer time for making hot water.

A further advantage consists in that the combustion channel 11 can,within a wide range, arbitrarily be arranged relative to the supplyopening 18 for primary air. The equipment can thus be better adapted tothe just existing conditions.

In the embodiment according to FIG. 4, the grate 15 is rotatable,whereas the grate scraper 27 is generally stationary. For this purpose,the pot-like grate 15 is connected with the gasifier ring 19 by means ofcarrier bolts 30, so that the grate 15 is taken along for rotation in asimilar manner as it is shown in FIG. 1 for the grate scraper 27. Thecarrier bolts 30 slide in longitudinal direction within vertical grooves39 provided on the circumference of the gasifier ring 19, so that heightadjustment of the grate 15 relative to the gasifier ring 19 is possible.In this case, the grate 15 is rotatably suspended on the central rod 24,the upper end of which is suspended by means of a friction coupling 64on a housing 46 of a worm gear 47. For this purpose, the rod 24 is fixedto a fiction disc 40 being located between two friction plates 41 whichare pressed one against the other by springs 42. The springs 42 surroundcolumns provided on the cover wall of the housing 46, which columns alsoserve for securing the two friction plates 41 against rotation. Thus, innormal operation, the friction disc 40 is subjected to a braking actionsuch that the rod 24 is not rotated and the grate scraper 27 fixed tothis rod remains at rest. In this case, the grate scraper 27 consits ofa horizontal transverse shaft 43 fixed to the rod 24, two flaps 44 beingarranged for swivelling motion around this transverse shaft, each ofsaid flaps carrying at its lower end a horizontal grate scraper bar 28sliding over the downwardly enlarged openings of the grate 15. If aminor obstacle or a temporary obstacle is encountered, the grate scraperflaps 44 can swivel around their horizontal transverse shaft 43 untilthe obstacle has been removed. If a permanent obstacle is encountered,the transverse shaft 43 is, however, given a rotating movement by thegrate 15 via the flaps 44 as soon as the friction resistance between thefriction disc 40 and said both friction plates 41 acting on the frictiondisc has been overcome.

Below the friction discs 41 there is arranged on the outer side of thehollow shaft 21 an adjusting nut 45 on a threaded part of the hollowshaft 21, said adjusting nut 45 being arranged such that it can abut onthe housing 46 of a worm gear 47 via which the hollow shaft 21 isrotated by the geared engine 22. This provides the possibility to adjustin heigt direction the hollow shaft 21 and also the gasifier ring 19suspended to this hollow shaft 21 by means of struts 20. In thisembodiment, the struts 20 carry resilient prongs 35, upwardly andobliquely directed into the storage compartment 4. The storagecompartment 4 is delimited by a sheet metal housing 5 being seatedwithin a clamping ring 48 holding together a plurality of sectors of aring 49 which consists of mineral material, for example of brick, andsurrounds the upper portion of the gasifier ring 19 and delimits withits downwardly and inwardly inclined top surface 50 a zone of coking gasformation. This zone extends up to the cover wall 6 of the storagecompartment 4, in which there is provided an opening 51 having annexedthereto a transverse channel 52 leading to a secondary air channel 53being open at its upper side. An adjusting flap 54 is arranged where thetransverse channel 52 merges into the secondary air channel 53, whichflap provides the possibility to adjust the ratio of the coking gasesflowing from the transverse channel 52 into the secondary air channel 53relative to the secondary air. The secondary air channel 53 opens intothe combustion channel 11.

Furthermore, a vertical coking gas channel 55 extends within the storagecompartment 4 from the uppermost area thereof till a horizontal channel56 provided within the mantle 9 consisting of concrete. This channel 56leads from an entry opening 57 for the supply of fresh air to thefurnace chamber 10 located above the grate 15. In this channel 56 thereis provided a heat insulating plate 66. A channel 58 is branched offfrom the channel 56 for the purpose of supplying fresh air into the ashchamber 16 located below the grate 15, this fresh air being pre-heatedby the heat shielding plate 66. The channel 56 enables one to clean thefurnace chamber 10.

The concrete mantle 9 is surrounded by an insulating mantle 59 which issurrounded at its outer side by a cavity 60. This cavity 60 has an inletopening 61 for fresh air and is in connection with a recess 62 beingprovided within the brick ring 49 above the combustion channel 11. Thisrecess 62 is in connection with the combustion channel 11 via a verticalchannel 63.

A lid 33 is provided on the opening 57 and is adjusted by the draughtregulator 3 of the boiler. A similar control means can be provided forthe air inlet opening 61.

Within the embodiment according to FIG. 4, primary air can be suppliedto the zone above the grate 15 as well as to the zone below the grate,for example of a small opening (not shown) is provided in the heatshielding plate 66. Because the lower most section of the gasifier ring19 neighbours the combustion chamber 10, the gasifier ring is very hotin this section so that the combustion material contacting this gasifierring 19 is already inflamed. In direction towards above, the gasifierring 19 becomes cooler, however de-gases the combustion material. In theuppermost section of the gasifier ring 19 and in the region of the ring49 the combustion material is dried and, in most cases, also degased.

The embodiment according to FIG. 4 is particularly suitable for bigequipment due to the big cross section of the storage compartment 4.

I claim:
 1. A combustion equipment for the combustion of solid combustible material of high ash content, comprising a furnace chamber having a grate at its bottom and receiving the combustible material from a storage compartment disposed above said furnace chamber, a mantle of refractory material surrounding said furnace chamber, a combustion channel for connecting said furnace chamber to a boiler means, said combustion channel extending through said mantle and having an opening for supplying secondary air, a further opening in the mantle for supplying primary air below the grate, a gasifier ring near said mantle and above said combustion channel and spaced at a distance above said grate, said gasifier ring having an upright axis and a central opening and a top surface, said top surface being inclined towards said central opening, a worm means extending in direction towards this opening and a drive means for rotating said gasifier ring around its axis, so that said worm means conveys the combustible material through said opening of the gasifier ring.
 2. A combustion equipment as claimed in claim 1, wherein said worm means extends through said opening of said gasifier ring.
 3. A combustion equipment as claimed in claim 1, wherein said worm means is stationary and held at its upper end by a rod located within a hollow shaft connected to said gasifier ring and being driven for rotation by said drive means.
 4. A combustion equipment as claimed in claim 1, wherein said drive means comprises a gear engine for intermittently rotating said gasifier ring.
 5. A combustion equipment as claimed in claim 3, wherein said hollow shaft is adapted for movement of laterally protruding projections arranged within said storage compartment.
 6. A combustion equipment as claimed in claim 5, wherein said projections are resilient prongs.
 7. A combustion equipment as claimed in claim 1, wherein said gasifier ring is arranged for being lifted and lowered in order to change its distance from the grate.
 8. A combustion equipment as claimed in claim 1, further comprising a grate scraper sliding over the grate.
 9. A combustion equipment as claimed in claim 8, wherein said grate scraper comprises at least one bar sliding over the grate.
 10. A combustion equipment as claimed in claim 8, wherein said grate scraper is connected to the gasifier ring.
 11. A combustion equipment as claimed in claim 10, wherein the grate scraper has vertical carrier bolts being guided within openings of the gasifier ring for being shifted in longitudinal direction.
 12. A combustion equipment as claimed in claim 7, wherein said worm means extends in the lowermost position of the gasifier ring into the hollow shaft for the length of the stroke of the gasifier ring.
 13. A combustion equipment as claimed in claim 1, wherein said gasifier ring has a triangular cross section and consists of fire brick, a collar being connected to the underside of said ring and extending downwardly from the opening of the gasifier ring.
 14. A combustion equipment as claimed in claim 1, wherein said worm means comprises a worm consisting of a twisted metal strip.
 15. A combustion equipment as claimed in claim 1, wherein the grate is suspended on the worm means and can be lifted and lowered together with this worm means.
 16. A combustion equipment as claimed in claim 1, wherein the grate is coupled to the gasifier ring for common rotation
 17. A combustion equipment as claimed in claim 16, wherein the grate has vertically extending rods guided for longitudinal movement in recesses on the periphery of the gasifier ring.
 18. A combustion equipment as claimed in claim 8, wherein the grate scraper is connected to a rod carrying the worm means.
 19. A combustion equipment as claimed in claim 18, wherein the rod is supported on its upper end by means of a friction coupling.
 20. A combustion equipment as claimed in claim 1, further comprising a ring consisting of mineral material and positioned near the gasifier ring, said ring having a top surface which is inclined towards the gasifier ring.
 21. A combustion equipment as claimed in claim 20, wherein the ring consists of at least two sectors held together by means of a metallic clamping ring.
 22. A combustion equipment as claimed in claim 1, further comprising at least one channel for coking gases which leads from the storage compartment to a further channel connected to the combustion chamber. 